Captain Rainbow is a rather odd Japan-only game based around an island populated by Nintendo's more obscure characters, many of whom hadn't had their games released outside Japan.
Oh, and there's a quest where Birdo's in jail for going into the wrong bathroom, where you prove she's female by way of an unknown vibrating thing (displayed as a question mark), something which probably also had a hand in the game not getting an international release.
A placeholder image with "dummy" slapped onto it.
A fully animated model of Mach Rider, seemingly depicted as female, is in the game, both on and off her motorcycle.
Any way of accessing these in-game?
There are two areas in the map data named "dummy" and "test".